Mated circular electrical connectors (that carry electrical currents or light waves) are often held together by a coupling nut rotatably mounted on the body of a first connector and which engages a thread on the second connector. A cover can be placed around the coupling nut to prevent turning it relative to the first connector body, so as to prevent unauthorized disconnection. A common type of cover is a heat shrinkable tubing slipped onto one of the connectors before mating, and which is later slipped over the coupling nut and connector body and heated to shrink it in place. Heat shrink tubing has disadvantages, including the fact that it is used only once, the connector may be nicked when the tubing is cut off, and heat required to shrink the tubing is not usable in an explosive atmosphere. Other types of covers have been proposed, such as a Velcro band, but no known covers have been satisfactory. A cover which could be rapidly installed and removed from a connector, and which was of simple design, would be of considerable value.